Sunday, August 26, 2012

Telephone Generation


Telephones have gone through three distinct generations, with different technologies:
1. Analog voice.
2. Digital voice.
3. Digital voice and data (Internet, e-mail, etc.).
First-Generation Mobile Phones: Analog Voice:
Enough about the politics and marketing aspects of mobile phones. Now let us look at the technology, starting with the earliest system. Mobile radio telephones were used sporadically for maritime and military communication during the early decades of the 20th century. In 1946, the first system for car-based telephones was set up in St. Louis. This system used a single large transmitter on top of a tall building and had a single channel, used for both sending and receiving.
To talk, the user had to push a button that enabled the transmitter and disabled the receiver. Such systems, known as push-to-talk systems, were installed in several cities beginning in the late 1950s. CB-radio, taxis, and police cars on television programs often use this technology.
In the 1960s, IMTS (Improved Mobile Telephone System) was installed. It, too, used a high-powered (200-watt) transmitter, on top of a hill, but now had two frequencies, one for sending and one for receiving, so the push-to-talk button was no longer needed.

Second-Generation Mobile Phones (2G): Digital Voice:
The first generation of mobile phones was analog; the second generation was digital. Just as there was no worldwide standardization during the first generation, there was also no standardization during the second, either. Four systems are in use now: D-AMPS, GSM, CDMA, and PDC. PDC is used only in Japan and is basically D-AMPS modified for backward compatibility with the first-generation Japanese analog system. The name PCS (Personal Communications Services) is sometimes used in the marketing literature to indicate a second-generation (i.e., digital) system. Originally it meant a mobile phone using the 1900 MHz band, but that distinction is rarely made now.

Third-Generation Mobile Phones (3G): Digital Voice and Data
What is the future of mobile telephony? Let us take a quick look. A number of factors are driving the industry.
First, data traffic already exceeds voice traffic on the fixed network and is growing exponentially, whereas voice traffic is essentially flat. Many industry experts expect data traffic to dominate voice on mobile devices as well soon.
Second, the telephone, entertainment, and computer industries have all gone digital and are rapidly converging. Many people are drooling over a lightweight, portable device that acts as a telephone, CD player, DVD player, e-mail terminal, Web interface, gaming machine, word processor, and more, all with worldwide wireless connectivity to the Internet at high bandwidth.
More realistic is 2 Mbps for stationary indoor users (which will compete head-on with ADSL), 384 kbps for people walking, and 144 kbps for connections in cars. Nevertheless, the whole area of 3G, as it is called, is one great cauldron of activity. The third generation may be a bit less than originally hoped for and a bit late, but it will surely happen.
The basic services that the IMT-2000 network is supposed to provide to its users are:
1. High-quality voice transmission.
2. Messaging (replacing e-mail, fax, SMS, chat, etc.).
3. Multimedia (playing music, viewing videos, films, television, etc.).
4. Internet access (Web surfing, including pages with audio and video).
Additional services might be video conferencing, telepresence, group game playing, and m-commerce (waving your telephone at the cashier to pay in a store). Furthermore, all these services are supposed to be available worldwide (with automatic connection via a satellite when no terrestrial network can be located), instantly (always on), and with quality-of-service guarantees.

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